Class EDOSelectedModel

This class encapsulates the data model for the flag
indicating whether an editable domain object (EDO) is selected
from a set of EDOs in an EDOHolderModel. One and only one
EDO can be selected at a time. This model also keeps track
of which EDO is selected.
If a new EDOHolder is selected (thus loading new data)
"this" gets reset to false (i.e nothing selected).
Version: 2.0